5 Essential ACL Tests Before Return to Sport –

How We Keep Our Athletes Safe

By: Tanner Bishop

Physiotherapist, CSCS, MSc PT, BSc Kine, NCCP Coach

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Tearing your ACL is one of the most significant injuries an athlete can face. Surgery is only the beginning; what happens during rehab determines whether you get back to sport safely and return to your best.

At FORTE, we follow a rigorous, evidence-based approach to return-to-sport testing. We don’t guess when you’re ready. We test, we measure, and we make sure. Here are the 5 criteria we assess for a safe return to sport.

 

No. 1: Timeline, A Minimum of 9 Months Post-Surgery

Your new ACL graft needs time to heal, mature, and integrate with your body. We respect that biology.

Research shows athletes who return before 9 months have a 7x higher rate of re-injury compared to those who wait. For every month return is delayed (up to 9 months), re-injury risk drops by roughly 51% per month.

That said, we don’t have you sitting around waiting for sport exposure. From 6 to 9 months, we progressively introduce sport-specific drills: running, cutting, jumping, and sport-simulated activities.

Our goal is to have you arrive at 9 months fully prepared, not just having “waited long enough.”

 

No. 2: Quadriceps & Hamstring Strength Testing

Your quads are the most commonly weakened muscle after ACL surgery. Only about 43% of patients achieve adequate quad strength symmetry by 6 months, which is why we test, not assume.

We require at least 90% Limb Symmetry Index (LSI), meaning your surgical leg produces at least 90% of the force your healthy leg does. Both quadriceps and hamstrings must meet this threshold.

Patients who achieve ≥90% quad LSI perform similarly to uninjured individuals, while those below 85% show measurable functional deficits.

We also assess absolute strength relative to your bodyweight, not just symmetry, because your “healthy” leg can lose strength during recovery too, making the LSI look artificially good.

Why we test this: Weak quads change the way you run, jump, and land, putting your knee in vulnerable positions. Strength symmetry is one of the strongest protective factors against re-injury.

 

No. 3: Drop Jump Testing (Reactive Strength Index)

Sport demands that your knee absorb force and redirect it instantly. We measure that ability using VALD’s force deck technology.

We analyze your Reactive Strength Index (RSI) = jump height ÷ ground contact time.

The minimum thresholds we follow for field sport athletes:

    – Bilateral (double leg): RSI > 1.3

    – Single leg: RSI > 0.5

We also look for >90% symmetry in jump height and both concentric and eccentric impulse.

Why we test this: Sport rarely gives you time to think. This test captures your knee’s ability to react under rapid, high-force conditions, closely mimicking the demands that caused the original injury.

No. 4: ACL-RSI (Psychological Readiness Questionnaire)

Physical readiness is only half the equation.

We use the ACL-RSI, a validated 12-item questionnaire measuring your emotional readiness, confidence in your knee, and perceived risk of re-injury. Scored 0 to 100.

Your mindset directly affects how you move. Research shows a U-shaped relationship between scores and re-injury risk:

Too low (~56 to 61): Reflects high fear, movement avoidance, and lack of confidence, leading to altered landing mechanics, reduced muscle activation, and hesitation during play.

Too high (~81+): May reflect overconfidence and underestimation of risk, leading to reckless return before the body is truly ready.

We monitor this throughout your rehab so we can address psychological barriers early, not just at the finish line.

Why we test this: Fear makes you move differently. Overconfidence makes you move carelessly. Both put your knee at risk. We want you confident AND realistic.

 

No. 5: Triple Hop Test

We have you hop forward three consecutive times on one leg and measure total distance on each side.

We require a minimum 90% LSI compared to the uninjured side.

We’re transparent about its limitations:

Athletes can achieve symmetrical hop distances while still having significant deficits in the surgical knee. Compensation through hip strategy or shorter hops on the healthy side can mask true weakness. This is why we never use this test in isolation. It is one piece of a larger picture.

As part of our broader test battery, the triple hop helps us assess your horizontal power, acceleration, and multi-joint coordination.

Why We Hold These Standards

The landmark Delaware-Oslo ACL Cohort Study found that passing criteria combining time, strength, and function reduced re-injury risk by 84%.

Kyritsis et al. (2016) found athletes who did not meet clinical discharge criteria had a 4x greater risk of graft rupture.

Each test addresses a different piece of the puzzle: biological healing, strength, reactive ability, psychological readiness, and functional power. We test all five because no single measure tells the whole story.

Our commitment is simple: We ensure you are fully prepared for your return to sport. That is how we keep our athletes safe and performing at their best.

 

References

• Grindem H, Snyder-Mackler L, Moksnes H, Engebretsen L, Risberg MA. Simple decision rules can reduce reinjury risk by 84% after ACL reconstruction: the Delaware-Oslo ACL cohort study. Br J Sports Med.2016;50(13):804-808.Ovid(WK)

Supports: 51% risk reduction per month delayed up to 9 months; 84% overall risk reduction with decision rules; quadriceps symmetry and RTS criteria

• Beischer S, Gustavsson L, Senorski EH, et al. Young athletes who return to sport before 9 months after ACL reconstruction have a rate of new injury 7 times that of those who return later. Br J Sports Med. 2020;54(18):1117-1123. (Referenced inBrJSpMed(BJSM)+1)

Supports: 7x higher re-injury rate for return before 9 months

• Grindem H, Engebretsen L, Axe M, Snyder-Mackler L, Risberg MA. Activity and functional readiness, not age, are the critical factors for second anterior cruciate ligament injury: the Delaware-Oslo ACL cohort study. Br J Sports Med. 2020;54(18):1099-1102.Ovid(WK)

Supports: Passing RTS criteria independently associated with lower second ACL injury rate

• Schmitt LC, Paterno MV, Hewett TE. The impact of quadriceps femoris strength asymmetry on functional performance at return to sport following anterior cruciate ligament reconstruction. J Orthop Sports Phys Ther.2012;42(9):750-759. (Referenced inNatureRevEndocrinology)

Supports: 90% quad LSI as recommended RTS criterion; functional deficits below 85% LSI

• Kotsifaki R, Van Rossom S,”; et al. Aspetar clinical practice guideline on rehabilitation after anterior cruciate ligament reconstruction. Br J Sports Med. 2023;57(9):500-514.BrJSpMed(BJSM)+1

Supports: RSI thresholds (>1.3 bilateral, >0.5 single leg); >90% symmetry in jump height and impulse; isokinetic strength criteria; overall RTS criteria

• Kotsifaki A, Whiteley R, Hansen C, et al. Single leg hop for distance symmetry masks lower limb biomechanics: time to discuss hop testing validity after ACL reconstruction. Br J Sports Med. 2022;56(5):249-256.BrJSpMed(BJSM)

Supports: Hop distance LSI can mask biomechanical deficits; athletes compensate via hip strategy

• Kotsifaki A, Whiteley R, Van Rossom S, et al. Single leg vertical jump performance identifies knee function deficits at return to sport after ACL reconstruction in male athletes. Br J Sports Med. 2022;56(9):490-498.BrJSpMed(BJSM)+1

Supports: Jump height and RSI better identify interlimb differences than hop distance; vertical jump testing recommended for RTS decision-making

• Kyritsis P, Bahr R, Landreau P, Miladi R, Witvrouw E. Likelihood of ACL graft rupture: not meeting six clinical discharge criteria before return to sport is associated with a four times greater risk of rupture. Br J Sports Med.2016;50(15):946-951.ScienceDirect+2

Supports: 4x greater graft rupture risk when discharge criteria not met

• McPherson AL, Feller JA, Hewett TE, Webster KE. Psychological readiness to return to sport is associated with second anterior cruciate ligament injuries. Am J Sports Med. 2019;47(4):857-862. (Referenced inBMCSportsSciMedRehab)

Supports: ACL-RSI score and second ACL injury association; U-shaped relationship between psychological readiness and re-injury

• Losciale JM, Zdeb RM, Ledbetter L, Reiman MP, Sell TC. The association between passing return-to-sport criteria and second anterior cruciate ligament injury risk: a systematic review with meta-analysis. J Orthop Sports Phys Ther. 2019;49(2):43-54. (Referenced inBrJSpMed(BJSM))

Supports: Limitations of hop tests in isolation; importance of multi-criteria test batteries

• Wiggins AJ, Grandhi RK, Schneider DK, Stanfield D, Webster KE, Myer GD. Risk of secondary injury in younger athletes after anterior cruciate ligament reconstruction: a systematic review and meta-analysis. Am J Sports Med. 2016;44(7):1861-1876.Ovid(WK)

Supports: 23% secondary ACL injury rate in young athletes returning to sport; younger age and activity level as risk factors

• Paterno MV, Thomas S, VanEtten KT, Schmitt LC. Confidence, ability to meet return to sport criteria, and second ACL injury risk associations after ACL-reconstruction. J Orthop Res. 2022;40(1):182-190. (Referenced inSportsMedOpen)

Supports: High self-reported confidence combined with passing RTS criteria associated with increased second ACL injury risk (overconfidence relationship)

• Webster KE, Feller JA. Exploring the high reinjury rate in younger patients undergoing anterior cruciate ligament reconstruction. Am J Sports Med. 2016;44(11):2827-2832.Ovid(WK)

Supports: High rates of graft rupture and contralateral injury in younger athletes

• Piussi R, Simonson R, Forssblad M, Beischer S, Thomeé R, Hamrin Senorski E. Combining return to sport, psychological readiness, body mass index and age to predict second ACL injury risk. Knee Surg Sports Traumatol Arthrosc. 2023. (Referenced inESSKAJournals(Wiley))

Supports: Low (<47.1) and high (>87.9) ACL-RSI scores as risk factors for second ACL injury (U-shaped relationship)

• Return to sport (RTS) tests and criteria following an anterior cruciate ligament (ACL) reconstruction (ACLR): a scoping review. The Knee. 2025;57:179-199.ScienceDirect

Supports: ≥90% LSI as most common threshold across studies; variability in RTS protocols; need for standardization